Gene Pools and Allele Frequency

Allele Frequency changes

allele frequency remains stable => gene is not evolving

allele frequency changes => is evolving

Adaptive alleles versus harmful mutations

Adaptive alleles:

Describe how gene flow alters allele frequency

• Define gene flow: the movement of alleles into or out of a population due to immigration and emigration

• gene flow is more likely to have a strong effect on allele frequencies on small populations compared to large ones

Describe how non random mating changes allele frequency

• Mates are chosen based on genetic traits, such as sexual selection

• mating more often with close neighbors than wit distant members of the population

• organisms choose mates that are most likely themselves => larger expression of that genotype

Describe how genetic drift alters allele frequency

• some individuals may, by cane, leave behind a few more offspring than oters

• the genes of the next generation will be the genes of the “lucky” individuals, not necessarily the better adapted inviduals

• when the population size is small, its more evident

Selection changes allele frequency

• te frequency of the dominant allele is increasing over time, suggesting that it provides an advantage in survival or reproduction for inviduals which possess it

• the frequency of the recessive allele is decreasing over time, suggesting that it provides a disadvantage in survivals or reproduction for inviduals which possess it

Differentiate and describe stabilizing selection, disruptive selection, and directional selection wit graphs

Example of Stabilizing selection: Birth Weight

Stabilizing favors the middle away from extremess

Directional selection favors penotypes at one extreme of the phenotypic rane, common during periods of environmental change => bell curve shirts in the direction of the selected phenotype

Examples of Directional selections: Darwin’s finches

Disruptive selection: favors invidiuals with phenotypes at both extremes of a phentypic uhh idk

Example of disruptive selection: Male Coho Salmon and their “hook nose” and “jack”

Hardy-Weinberg Equilibrium

• used if a population is NOT evolving (if the allele frequency is not changing)

• P= dominant allele, q= recessive allele, p+q= 1

• When there are two alleles: p² + 2pq + q² = 1

Conditions for HW

• allele frequencies cannot be changing

Assumptions/ conditions

1) large populations (not work well with small ones => too much possible change)

2) No migration/ geneflow

3) No mutations

4) Has to be random mating

5) No natural selection

Stickleback back fish

• in the ocean: have spines, 440 (Dom)

• in lake: spinless, 64 (Rec)

• calculate allele frequency and genotype and phenotype

Speciation

• the process by which a population of one species diverges to become two distinct species (see IB definition of it)

• => over time they can becomes two separate different species from one another

• gradual evolutionary change in a species over time is not speciation

how do we get to speciation

1) reproductive isolation; can be geographical, behavioral, or temporal

2) Differential selection: caused by selective pressures